General Chemistry

Amino Acids: The Building Blocks of Proteins

All proteins consist of chains of amino acids. An amino acid (Figure 3) is a molecule containing a central carbon atom and three special functional groups: a carboxylic acid group (—COOH), an amino group (—NH2), and variable "side chain" (generically denoted by "R").  (Note:  The "—" in  "—COOH" and "—NH2" indicates a bond to another atom in the rest of the molecule.)  There are 20 different amino acids that are available to be incorporated into proteins. The side chains of the 20 amino acids have different properties, which in turn give different properties to the amino acids. For instance, side chains may be charged (e.g., glutamate) or electrically neutral (e.g., leucine), bulky (e.g., tryptophan) or consisting only of a hydrogen atom (glycine).

Amino Acid Leucine

Figure 3

On the left is a two-dimensional ChemDraw model of an amino acid. The carboxylic acid group is shown in blue, the amino group is shown in purple, and the central carbon atom is shown in red. The green "R" represents the side chain, which is different for each amino acid.

On the right is a two-dimensional ChemDraw model of leucine, one of the twenty amino acids available for building proteins. Leucine differs from the other amino acids only in its side chain, shown in green.

 


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Revised: 2004-08-08